The use of communication-enabled mobile computing devices (or mobile devices for short), such as cellular telephones, personal digital assistants (PDAs), netbook computers, cars, airplanes and so on, has become quite common. Typically, devices of this type are capable of using on-board sensors to capture sensor data that can be used to determine the location of the device. For example, these devices are often capable of recording cell-phone or radio tower strength measurements, Wi-Fi network strength data, and satellite Global Positioning System (GPS) data, as well as other types of data that can be used to determine location.
Knowing the location of mobile devices makes it possible to provide a variety of location-based services to mobile device users. For example, members of both formal and informal (ad-hoc) groups of mobile device users would like to know if other group members are geographically close so that they can meet or interact via their mobile devices. This is particularly useful when these users are travelling and are not familiar with other group members that may be in the area.